Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$55.52	3.567%	$57.5004	$57.50	$57.50	$57.50
Purchase #2	$104.93	6.198%	$111.4336	$111.43	$111.45	$111.40
Purchase #3	$230.32	5.254%	$242.421	$242.42	$242.40	$242.40
Purchase #4	$153.97	5.124%	$161.8594	$161.86	$161.85	$161.90
Purchase #5	$98.72	13.264%	$111.8142	$111.81	$111.80	$111.80
Purchase #6	$175.31	11.407%	$195.3076	$195.31	$195.30	$195.30
Purchase #7	$202.69	12.472%	$227.9695	$227.97	$227.95	$228.00
7 purchase totals =	$1,021.46		$1,108.3057	$1,108.30	$1,108.25	$1,108.30